(a) Field of the Invention
The invention relates to the development of a new strain of Sporothrix flocculosa resistant to the fungicide dodemorph-acetate and its use as a biofungicide in integrated pest management.
(b) Description of Prior Art
Despite the development of various strategies of pest control (Batra, S. W. T., 1982, Science, 215:134-139), the use of synthetic chemical pesticides have predominated since 1950. However, the adverse environmental consequences in using certain toxic chemical pesticides, the development of resistance by certain pests to chemical pesticides and the increasing production costs for new compounds are currently encouraging greater interest in biological control agents (Mukerji, K. G., and Garg, K. L., 1988, Biocontrol of Plant Disease, Vol. I., CRC Press, Boca Raton, Fla.; Payne, C. C., 1988, Phil. Trans. R. Soc. Lond. B, 318:225-248).
Powdery mildew fungi are important plant diseases for which the control relies heavily on fungicides. This trend could be modified in light of the discovery of a number of hyperparasites and antagonists against these fungi (Hijwegen, T., and H. Buchenaeur, 1984, Neth. J. Plant Pathol., 90:79-84). For instance, Tilletiopsis Berx species have been found to control Erysiphe graminis DC var. hordei Em. March. (Klecan, A. L. et al., 1990, Phytopathol., 80:325-331), Sphaerotheca fuliginea (Schlecht.:Fr.) Poll. (Hijwegen, T., 1986, Neth. J. Plant Pathol., 92:93-95), as well as other powdery mildews (Hijwegen and Buchenauer, 1984, idem). In addition, recent studies have shown that a yeast like fungus, Sporothrix flocculosa (Traquair, Shaw & Jarvis; Traquair, J.A. et al., 1988, Can. J. Bot., 66:926-933) antagonized the powdery mildew pathogen of cucumber (Jarvis, W.R. et al., 1989, Mycol. Res., 92:162-165) and rose (Hajlaoui, M.R. et al., 1991, Neth. J. Plant Pathol., 97:203-208). When applied at the rate of 1.times.10.sup.6 spores/ml under controlled conditions, Sp. flocculosa reduced powdery mildew colonies on leaves of rose within a 48-hour period (Hajlaoui and B elanger, 1991, idem). When used under commercial conditions, Sp. flocculosa proved as effective as fungicides at controlling rose powder mildew (B elanger, R. R. et al., 1994, Plant Disease, 78(4):420-424).
One of the major constraints in the use of a biofungicide is its own susceptibility to fungicides currently used in the crops to protect them (Papavizas, G. C., 1983, Phytopathology, 73:407-411). With the current scheme of integrated control of plant diseases, the combination or alternance of natural and chemical fungicides is a very appealing strategy to optimize both disease control and protection of the environment. However, this approach presupposes that the biocontrol agent is resistant to the fungicide used for the particular disease to control. Therefore, development of a Sp. flocculosa strain resistant to fungicides used in the control of powdery mildew would allow the integrated use of biological and chemical approaches in a disease management scheme.
It would be highly desirable to be provided with a strain of Sp. flocculosa resistant to important fungicides registered for the control of powdery mildew.